Many direct access storage device manufacturers employ thin film magnetic recording heads. In manufacturing such heads, rows of magnetic recording transducers are deposited simultaneously on wafer substrates using semiconductor type process methods. Thin film magnetic heads are generally mutli-layered heads that require sequential depositions and pattern constructions of alternating layers of magnetic films, insulators, and conductors on top of a substrate (or ceramic wafer). Photolithography is the process commonly used to transfer a pattern from a mask to the surface of the substrate wafer. The patterns are first transferred from the mask to a light-sensitive material called photoresist. Next, chemical or plasma etching is used to transfer the pattern from the photoresist to a barrier material on the surface of the wafer. The photolithographic process is repeated to form the various layers of the thin film heads.
After the rows of magnetic recording transducers have been deposited onto the wafer, the wafers are partitioned or sliced into rows of sliders called slider rows, or alternatively, partitioned or sliced into modules having multiple rows of sliders. When separated from the slider rows, each slider contains a magnetic read/write component, referred to as the head, and an air-bearing surface configured to aerodynamically "fly" over the surface of a spinning magnetic disk medium. Conventional thin film read/write heads in data storage systems generally include an inductive write head in combination with either an inductive or magnetoresistive (MR) read head. One type of MR/inductive head includes an inductive write head formed adjacent to a MR read head.
While fabricating sliders, the slider rows or modules may be bonded to tool blocks called transfer tools, which are used to hold the slider row or module while performing lapping or grinding operations to form the air bearing surface. Typically, the slider rows distort from a co-linear line as a result of the internal stress of the wafer material and the surface stresses developed when reducing the wafers to slider rows or modules. Furthermore, the bonding operation may cause additional distortion. The combined stress distortion and bonding distortion of slider rows or modules may result in a total distortion or curvature condition called "row bow".
Row bow may cause a row of sliders to be non-uniformly lapped during the lapping process. As such, this row bow condition can detrimentally affect critical head performance parameters, such as stripe height in MR heads, and throat height in inductive heads. To achieve optimum performance of MR/inductive heads, both the stripe height and throat height must be tightly controlled. Unfortunately, the performance of the MR/inductive heads may be degraded by row bow.
The lapping control system described in commonly assigned U.S. Pat. No. 4,914,868 may be used to measure the electrical resistance of the MR elements in an MR head while lapping a slider row. The measured resistances are used for controlling the degree of lapping for each of the MR elements in a slider row to compensate for row bow. The electrical resistance is related to the desired MR element height (also referred to as stripe height); and, when the desired MR element height is reached, the lapping process is terminated. More specifically, the stripe height of the MR element s is calculated from the equation: EQU s=K/(R-RL) (1)
where:
K=(resistivity p*track width 1)/(film thickness f) PA1 R=resistance of the MR element PA1 RL=lead resistance PA1 K=(resistivity p*track width 1)/(film thickness f) PA1 R=resistance of the MR element PA1 RL=lead resistance PA1 W=windage PA1 Hn=nominal height of an MR element PA1 H.sub.3 =Nominal height of resistive element 3 PA1 R.sub.1 =Resistance of resistive element 1 PA1 R.sub.2 =Resistance of resistive element 2 PA1 R.sub.3 =Resistance of resistive element 3.
In order to control the amount of lapping performed on a slider row and to accurately determine the final MR element height (at the conclusion of lapping), both K and RL must be known.
The lapping process may begin with two well-defined initial MR element heights, s1 and s2, interleaved throughout the row. In other words, the MR elements in a slider row are deposited on the wafer with alternating MR stripe heights s1 and s2. The MR element heights, s1 and s2, deposited on the wafer may be optically measured. Once the MR element heights s1 and s2 are known, the following equations may be used to calculate K and RL: EQU s1=K/(R1-RL) (2) EQU s2=K/(R2-RL) (3)
By providing MR elements with two known heights, the final resistance of the MR elements can be used to determine the final MR element height. Thus, the lapping process may be controlled by the resistance of the MR elements in a slider row.
It is important to note that if the MR element heights s1 and s2 are not known, then equations (2) and (3) alone, may not be used to calculate K and RL. Unfortunately, measuring the MR element heights s1 and s2 typically requires an additional processing step prior to the lapping operation.
An alternative lapping method that uses the resistance of the MR elements to control the lapping provides one or more test sites on a wafer for measuring the windage of the wafer. Windage atypically refers to the deviation in the dimensions of elements e.g., MR elements) deposited on a wafer from the dimensions of the mask (also referred to as the nominal value), which may result from the misalignment of masks or process variations.
The windage may be calibrated by actual measurements by a probe that provides substantially zero lead resistance RL. A calibration step is described in IBM Technical Disclosure Bulletin, Vol. 18, No. 11, April 1976, p. 3782. The calibration information must then be stored in a database for subsequent access and use in the lapping process. An alternative method for estimating the windage is mentioned in coassigned U.S. Pat. No. 5,361 541, at col. 9, line 65 to col. 11, line 3, again requiring a separate measurement step before lapping and requiring storage of data while awaiting multiple wafer and row processing steps before being employed in the lapping process. Once the windage is known, the following equation may be used to calculate K, assuming that RL is substantially zero. EQU R=K+RL/(Hn+W) (4)
where:
Once K is known, the MR element height (i.e., stripe height) may be determined from equation (1) . Thus, the measured resistance of the MR element may be used to control the amount of lapping of a slider row.
The separate windage calibration step prior to lapping is costly both from the standpoint of the extra time required to conduct the step, and from the standpoint of the computer data storage space and transmission required to save the data for a later calibration step. Additionally, the test sites are positioned on a wafer and occupy space that would otherwise be used for additional sliders and heads. Furthermore, the number of test sites are typically limited and cannot be positioned next to each MR location. The chance for error due to the few test sites and lack of close positioning may degrade the ability to accurately predict the MR stripe height at during lapping. Thus, it is much more desirable to determine windage directly at each element location during the lapping operation without a separate calibration step and without the use of test sites.